Influence Of Diffusion Coefficient Research Articles

Fission characteristics of heavy metal intrusion into rocks based on hydrolysis

Abstract The mechanism of hydrolysis and extension diffusion of heavy metal pollution elements infiltrated into rock is analyzed by the theory of ion hydrolysis displacement. The hydrolysis properties of typical elements such as cadmium, zinc, lead, and copper are verified by convective dispersion model, and the diffusion law and fission characteristics of heavy metal with different hydrolysis constant are discussed. A three-dimensional constitutive relation model of rock extension diffusion surface is established by combining viscoelastic monomer model with a damage monomer model. Considering the influence of diffusion coefficient, hydrolysis constant, deformation factor, and other parameters, the rationality of the test results and model fitting results of heavy metal invading rock are verified. The results show that the replacement rate of colloidal mineral elements in rock varies with different hydrolysis constant, when the hydrolysis constant is large, the extension diffusion rate in rock is large; otherwise, the extension diffusion rate is small. Constitutive relation curves of polluted rock with different lithologies are in good agreement with the fitting results of the combination model under the influence of the same test conditions and the same parameters.

Spatial dynamics and optimization method for a rumor propagation model in both homogeneous and heterogeneous environment.

Considering the influence of environmental capacity and forgetting on rumor spreading, we improve the traditional SIR (susceptible–infected–removed) rumor propagation model and give two dynamic models of rumor propagation in heterogeneous environment and homogeneous environment, respectively. The main purpose of this paper is to make a dynamic analysis of rumor propagation models. In the spatial heterogeneous environment, we have analyzed the uniform persistence of the rumor propagation model and the asymptotic behavior of the positive equilibrium point when the diffusion rate of rumor–susceptible tends to zero. In the spatial homogeneous environment, we discuss the stability of rumor propagation model. Further, optimal control and the necessary optimality conditions are obtained by using the maximum principle. Finally, we study the Hopf bifurcation phenomenon through inducing time delay in the reaction–diffusion model. In addition, the existence of Hopf bifurcation is verified and the influence of diffusion coefficients is studied by numerical simulations.

Influence of Diffusion Coefficient of Cobalt Redox Mediator Using Triphenylamine Dyes with Various Number of Anchoring Groups: Photovoltaic Performance of DSSCs

The development of electrolytes containing a novel redox shuttle is essential for achieving highly efficient and stable dye-sensitized solar cells (DSSCs). Here, the effect of the diffusion coefficient of redox shuttles in the electrolyte on the photovoltaic performance of DSSCs using triphenylamine dyes by a different number of anchoring groups was investigated. Two different types of cobalt (II)/(III) polypyridine complexes, namely, [Co(bpy)3]2+/3+ and [Co(dtb)3]2+/3+ (where bpy = (2,2′-bipyridine) and dtb = (4,4′-di-tert-butyl-2,2′-bipyridine)), are applied to the hole transporting redox shuttles in DSSCs. Their diffusion coefficients are estimated by linear sweep voltammetry (LSV) at various scan rates. The diffusion coefficient of [Co(bpy)3]2+ and [Co(dtb)3]2+ in the prepared electrolyte are 1.91 × 10−7 and 2.27 × 10−8 cm2/s, respectively. The high diffusion coefficient of [Co(bpy)3]2+ leads to a high ionic conductivity of the electrolyte that is nearly two times higher than the [Co(dtb)3]2+/3+-based electrolyte. This [Co(bpy)3]2+/3+-based electrolyte leads to an increase in the DSSCs photovoltaic performance with an increase in electronic coupling with the organic dye and TiO2. This is due to the photovoltaic performance is not limited by the mass-transportation process.

Synchronization analysis for stochastic reaction-diffusion Cohen-Grossberg neural networks with Neumann boundary conditions via periodically intermittent control

In this paper, mathematical analysis is proposed on the synchronization problem for stochastic reaction-diffusion Cohen-Grossberg neural networks with Neumann boundary conditions. By introducing several important inequalities and using Lyapunov functional technique, some new synchronization criteria in terms of p-norm are derived under periodically intermittent control. Some previous known results in the literature are improved, and some restrictions on the mixed time-varying delays are removed. The influence of diffusion coefficients, diffusion space, stochastic perturbation and control width on synchronization is analyzed by the obtained synchronization criteria. Numerical simulations are presented to show the feasibility of the theoretical results.

Gas Flow Mechanism in Tight Reservoir and Productivity Prediction Model of Fractured Wells

Flow mechanism in tight reservoir is different from that in normal reservoir because of the nanoscale and micro-scale holes in the reservoir. Beskok-Karniadakis model can describe gas diffusion and flow. In this paper, Beskok-Karniadakis model was applied and optimized in consideration of the tight gas productivity influenced by both Knudsen diffusion and desorption. Furthermore, tight gass productivity of fractured vertical wells was obtained with the method of permeability resistance. In combination of examples and theory, the influence of diffusion coefficient, half-length of fractures and fracture conductivity on well gas productivity was analyzed. The results show that free gas has a close connection with total productivity. Diffusion coefficients are not the same in different reservoir, and this can also influence the productivity. For fracture conductivity, the productivity goes up with the fracture conductivity increases. A method to provide guidance of effective productivity is gotten with optimizing the conductivity.

Optimized Simulation for GaN Growth in Vertical HVPE Reactor

The paper reports the setting up of a model of fluid dynamic for GaN HVPE system and the simulation. The deposition of GaN with the variation of the gas flow inlet velocities is investigated. The influence of diffusion coefficient on the deposition of GaN is also discussed. It is found that the influence of the gas flow inlet velocities on the deposition is large and the influence of diffusion coefficient on the deposition of GaN is small in vertical HVPE.

Phase Field Simulation of Coarsening Kinetics in Al-Sc and Al-Sc-Zr Alloys

AbstractThe coarsening kinetics of γ’ precipitates in binary and ternary Al3Sc1-xZrx alloys is studied by using the two- and three-dimensional phase-field simulations. Our focus is on the influence of diffusion coefficients of Sc and Zr atoms on the transformation path kinetics from disordered f.c.c. matrix to two phases equilibrium state with γ’ precipitates and f.c.c. disordered matrix. Our simulation results demonstrate that in the case of binary alloys taking into account the concentration dependence of the mobility of atoms decreases the coarsening rate. In the case of ternary alloys we show that the Al3Sc particles precipitate first following by appearance of a Zr-rich shell. Our simulations results are in good agreement with experimental observations.

A method for computing diffusion coefficients in multiphase systems

Amethod for computing the effective values of diffusion coefficients in phases on the basis of a mathematical model of the process of diffusion saturation in multiphase systems is suggested. Diffusion coefficients are determined with the use of the results of solution of a direct diffusion problem. Regular features of the influence of diffusion coefficients on the thickness of phases in the diffusion zone are established.

The influence of diffusion coefficients in a catalytic electron transfer mechanism on linear sweep voltammetric and potential step chronoamperometric measurements

The kinetic equations for a catalytic mechanism consisting of a homogeneous electron transfer followed by two competing fast second-order reactions, a coupling reaction and a homogeneous electron transfer, are solved by digital simulation for linear sweep voltammetry and potential step chronoamperometry at a stationary planar electrode. The simulations allow determination of the first homogeneous electron transfer rate constant kET and a competition parameter q for the two follow-up reactions. The influence on the current of different ratios of the diffusion coefficients of the species involved was examined and it is shown that it can be rationalized from a combined “near-reversible”, steady-state and “total catalysis” approach. The lack of consideration of unequal diffusion coefficients may introduce errors in the experimental determination of the parameter q.

Photochemical reactions with a participation of diffusion

Influence of diffusion coefficients of reaction components on a course of simple photochemical reactions has been studied by numerical simulation. Diffusion coefficients have been varied in the range <0,∞>. Relationship between values of diffusion coefficients and parameters of photochemical reactions (entry concentrations and absorptivities of components, intensity of incident light and quantum yield of corresponding photochemical reactions) have been shown.

Approximate calculation of time-dependent behaviour of fluctuations in the presence of diffusion

Time-dependent behaviour of fluctuations for a reaction-diffusion system is analyzed using the multivariate master equation and neglecting the space correlations of order higher than two. The influence of diffusion coefficient is discussed. Only for a suitable diffusion rate and initial concentrations will the fluctuation be enhanced. Analytic results are compared with the numerical calculations.